1. Field of the Invention
This invention relates to semiconductor devices having a movable portion inside a chip, such as a capacity type acceleration sensor, a yaw rate sensor and a pressure sensor, and having a mechanically weak structure such as an air-bridge wiring structure, and to methods of manufacturing the same.
2. Description of the Related Art
A semiconductor wafer such as a silicon wafer on which several semiconductor integrated circuit elements are formed is usually cut by a dicing-cut device for individual semiconductor chips while being disposed on an adhesive sheet. The dicing-cut device requires a large amount of cutting water to remove undesirable silicon chips, radiate heat, and to facilitate the cutting.
However, when the elements to be divided include an element such as a capacity type acceleration sensor having a movable portion, or an element on which a mechanically weak structure such as an air-bridge wiring structure is exposed, such functional elements are easily broken by pressure and surface tension produced by the large amount of cutting water.
To solve this problem, JP-A-7-99172 proposes a method for dicing a silicon wafer while covering an exposed weak structure with a tape as a provisonal protective cap. The tape has an adhesive pattern to be attached to the semiconductor wafer. As a result of studies on this method, however, the following problems were found. Specifically, when the adhesive pattern is printed on the tape, a width of the pattern is, for example, 0.2 mm at least since it is limited by a mask material, printing conditions, and the like. When the tape is adhered to the semiconductor wafer, the adhesive pattern is further widended by pressure. The widened adhesive pattern may reach the exposed structure on the semiconductor wafer. When the adhesive pattern is formed with a large gap in consideration of the above problem, an area of the tape must be increased. The tape having the increased area is not suitable for an element having a reduced size. Thus, in the method disclosed in the above document, since the width of the adhesive pattern is varied when the adhesive pattern is adhered, it is difficult to securely protect the exposed structure on the wafer.
JP-A-9-27466 discloses another method for provisionally covering an exposed structure on a wafer with a adhesive sheet as a protective cap. The adhesive sheet is formed to have a dome portion for covering the exposed structure to prevent from being stuck to the exposed structure. This method involves difficulty for controlling the shape of the dome portion, and low productivity (through put) due to the formation of the dome portion performed by heating, and the like. Here, it should be noted that the protective caps disclosed in the documents described above protect the exposed structure not only during the dicing but also during transportation. The protective caps make the handling in the transportation easy.